A screwed joint for driven wheels of motor vehicles is described in DE 195 43 436 C2. The screwed joint connects a wheel flange to a drive element, for example to an articulation bell of a drive shaft, of the vehicle. With this joint, a rotationally fixed joint which consequently transmits torques from the drive element to the wheel flange is produced. The wheel flange is fixed to the vehicle and receives a bearing arrangement for a vehicle wheel.
A through-hole extends axially through the flange. A bolt-like extension of the drive element is introduced into the through-hole and is by means of the screwed joint connected to the wheel flange in a rotationally fixed manner and secured thereon. The rotary joint is alternatively produced by press connections, positive connections or preferably a combination of press and positive connections. The connections allow torques to be transmitted from the drive element to the flange and vice versa in the peripheral direction about the longitudinal central axis of the wheel flange. The joint is to be absolutely play-free.
The screwed joint is highly loaded. On the one hand, depending on bearing design, preloading forces for a play-free bearing are to be generated with the screwed joint and, on the other hand, the rotary joint and the axial retention of the drive element on the flange are to be secured.
During mounting of the drive element in the flange, the bolt of the drive element is to begin with introduced into the bore of the flange until a thread on the free end of the bolt protrudes on the other side of the hole. A nut is then screwed onto this thread to form a loose screwed joint with the bolt until the nut is supported axially on the flange.
The nut is then tightened. In the course of this, resistances on the bolt to the drive element being drawn into a press connection have to be overcome by rotation of the nut. These resistances arise by virtue of overlaps between the bolt-like extension of the drive element and the hole in the flange. Examples of such positive press connections are pairings of longitudinal toothings on the inside of the hole of the flange with longitudinal toothings on the outside of the bolt, which are additionally secured or rendered play-free by press fits in the tooth pairings. When the drive element is drawn into the flange, the nut is therefore axially supported on a supporting surface of the flange.
The axial resistances originating from the press connection are overcome by high tightening torques on the nut. High frictional moments arise between the nut and the supporting surface owing to the great tightening torques. The level of the tightening torques to be applied to the nut with an assembly device is therefore determined on the one hand by the level of the axial resistances to drawing-in and on the other hand by the frictional conditions between nut and guide surface plus the friction in the thread pairing.
The level of these tightening torques is difficult to assess as these forces are determined by various influencing factors such as manufacturing tolerances in the pairings and press connections and also by frictional losses of varying size. The tightening torque which is necessary in order to overcome these resistances can vary in the range of a desired tightening torque which is necessary in order effectively to secure the unit axially. It is therefore often not possible to distinguish whether the tightening torque on the nut measured directly or indirectly during screwing together has been brought about by the axial resistances which are difficult to calculate or by sufficient axial prestressing of the joint and of the bearing.
As the screwing tools as a rule switch off when the desired value of this tightening torque is reached, this frequently results in practice in the bearing or the rotary joint being inadequately prestressed. This leads to loosening of the screwed joint, to unacceptable play in the wheel bearing arrangement and/or to micromovements between the drive element and the flange. These micromovements give rise to noise and wear. The wear may cause indentations in the drive element which can lead to breakage of the drive element.